Safety controls for elevator door closing mechanism



March 11, 1958 BORDEN 2,826,272

SAFETY CONTROLS FOR ELEVATOR DOOR CLOSING MECHANISM Filed June 15, 1955 2 Sheets-Sheet 1 INVENTOR. g I JOSEPH H BURDEN I BY March 11, 1958 J. H. BORDEN 2,826,272

SAFETY CONTROLS FOR ELEVATOR DOOR CLOSING MECHANISM Filed June 15, 1955 2 Sheets-Sheet 2 HATCHWAY 000/? 59 as 85 a7 o as L 7 1Z7 INVENTOR- JOSE PH H BURDEN ATT IVEY United States Patent Ofilice Patented Mar. 11, 1558 SAFETY CONTROLS FOR ELEVATOR D0012 CLOSING MECHANlSll/l Joseph H. Borden, Toledo, Ohio, assigncr to Toledo Scale Corporation, Washington Township, Chic, a corporation of Ohio Application June 15, 1955, Serial No. 515,685

11 Claims. (Cl. 187-48) This invention is an improvement in safety controls for elevator car door closing mechanism. Passenger elevator car doorways and hoistway entrances usually are equipped with laterally sliding doors. A doorway may be either of the so-called center opening type, in which the doorway is at the center of the car or hoistway entrance and a pair of doors slide apart in opposite directions to open the doorway, or it may be of the so-called side opening type, in which the car doorway is at one side of the car and each hoistway entrance is at one side of the hoistway and one or more doors slide to the other side of the car and each hoistway entrance to open the doorways.

Side opening doors usually are in pairs, one of the doors of each pair traveling at twice the speed of its companion door so that, while a pair of doors can close a doorway the width of which is nearly two-thirds of the width of a car or hoistway, they overlap when open to occupy slightly more than one-third the width of the car or hoistway.

In modern elevator systems power operated mechanisms are employed to open doors automatically when cars arrive at hoistway entrances and to close doors before the cars depart. in systems the cars of which have no attendants passengers sometimes attempt to enter or leave after the doors have started to close. To prevent injury to passengers in such circumstances elevator door closing mechanism have been equipped with devices which sense the approach of leading edges of car doors to persons or other objects in the doorways and instantly act to stop or reverse the door movement.

Certain of such devices existing prior to the instant invention have a pair of plates mounted near the front edge of each car door the movement or" which is to be controlled and a voltage is impressed across the two plates thus establishing an electrostatic field in the doorway.

The plates are connected in a tuned circuit, one element of which is the capacity of the condenser formed by the said plates. The tuned circuit is inductively fed with alternating current with the frequency of which the tuned circuit is in resonance.

When a person or other object is in the electrostatic field surrounding the said plates the tuned circuit is detuned from resonance with the high frequency oscillations, the voltage across the inductance of the tuned cir cult is lowered and the output current is reduced. A relay in the output circuit responds to the reduction in the output current and in turn the relay so controls the door closing mechanism that the door movement is stopped or reversed (see for example U. S. patent to Lubkin No. 1,982,442, dated November 27, 1934).

In another type of safety control for elevator car door closing mechanism cold cathode tubes are mounted at vertically spaced intervals along the leading edge of the car door the movement of which is to be controlled, each tube being provided with an antenna which extends along a section of the leading edge of the door. A periodic source of current is so connected to the tubes as to fire any of them upon sufficient change of capacity to ground of the antenna of that tube, which change can be brought about by the approach of a person or object to the antenna. The tubes are so connected into the door closing mechanism controls that the firing of any tube prevents or reverses closing movement of the door. (See for example U. S. patent to Bruno et al. No. 2,601,250, dated June 24, 1952.)

Prior art devices of both the types mentioned above are highly sensitive to environmental influences such as changes in temperature, humidity, extraneous electrical conditions, etc. Even when their stability is bolstered by heaters to maintain constant temperatures, voltage regulators, compensatory capacitors and other adjuncts, such prior door movement safety controls are liable to failure.

It is an object of the instant invention to provide a safety control for elevator car door closing mechanism the reliability of which is substantially immune to the influences of vagaries of environment.

Another object is to provide a safety control for elevator door closing mechanism the reliability of which is unaflected by gradual changes within the control circuits or in neighboring conditions or in the positions of nearby bodies.

Another object is to provide a safety control for elevator door closing mechanism, which safety control functions in response to abrupt changes of antenna-to-ground capacity but is unaffected by gradual changes within or in proximity to the control circuits.

Another object is to provide such a control device which is sensitive to abrupt changes in capacity and which is capable of functioning with such capacity at various values prior to abrupt change.

Another object is to provide an elevator car door movement control device having antenna-to-ground capacity sensitivity combined with photoelectric sensitivity.

And still another object is to provide an electronic elevator car door control mechanism which is of sturdy and economical design and construction and which includes a simple antenna extending along substantially the entire leading edge of the elevator door.

Other objects, advantages and features of the invention will be apparent upon perusal of the following description of a preferred embodiment of the invention.

According to the invention an elevator car door is provided with an antenna wire carried as near to the leading edge of the door as practicable, preferably to the side of the leading edge which is toward a hoistway door when the car is at a hoistway entrance. The antenna is energized with an alternating current to create an electrostatic field extending ahead of the door edge.

Sensitivity and reliability may be enhanced by mounting a metallic U-shaped channel shield in back of the antenna oriented with its open side facing in the direction of door closing movement. The shield is carried by the car door and is energized with an alternating current generally in time phase with the current which energizes the antenna wire so as to reduce the effective capacity of the antenna and to make it more sensitive to capacity changes resulting from the presence of persons or objects in the path of the closing door. The antenna wire is connected to a detector circuit, similar to the detector circuit employed in a radio, arranged to deliver a variable direct current voltage that varies according to the proximity of foreign objects in the path of the leading edge of the door. The varying direct current voltage developed by the detector, after being filtered to eliminate the alternating current components of the antenna energizing frequency, is passed through one or more stages of resistance-capacitance coupled amplification and used to operate a control relay efiective to cause reopening of the doors. The time constants of the coupling circuits between the detector circuit and the first stage of the amplifier and between the amplifier Stages are adjusted to produce a differentiation of the output voltage of the detector stage so that only the varying component resulting from the relatively rapid approach of the leading edge of the door to an object is amplified and applied to the relay while slow changes in capacity between the antenna wire and the energized channel and changes in leakage current from the antenna wire which elfect the average voltage developed by the detector stage, are not amplified and therefore do not affect the relay.

A preferred circuit embodying the invention and arranged to cooperate with a door operating controi illustrated in the accompanying drawings.

In the drawings: 1

Fig. I is a diagram showing principal features of a preferred form of the invention.

Fig. II is an enlarged fragmentary diagramatic view taken in the direction indicated by the arrows IIII on Fig. IV showing the mounting of an antenna and its location with respect to a car door.

Fig. III is a simple diagram of door opening and closing circuits to which the safety control of the instant invention may be connected.

Fig. IV is a schematic elevational view of an elevator car showing door closing mechanism and the location of an antenna, a projector, and a light sensitive element.

The reliability and the proper functioning of the control of this invention is attainable, if size of equipment, consumption of power and other practical and economical considerations be neglected, with simple circuits and without meticulous selection of frequencies, capacities, resistances and other coordinated features. However, in this specification I have mentioned numerical values which enable the device of this invention to be constructed with readily available parts and to occupy conveniently small space and to function with conveniently and economically produced current.

Referring to Figs. I and II a U-shaped channel 1 of conductive material and mounted in casing of insulation 2 is arranged along the leading edge of an elevator car door 3, preferably on the side which is toward a hoistway door when the car is at an entrance. As may be seen in Fig. H the open side of the U-shaped channel 1 is closed by an insulating strip 4 in which an antenna wire 5 is mounted.

As shown in Figure I, the U-shaped channel 1, constructed of conductive material, is energized through a lead 6 which is connected to an output lead 7 of an oscillator 8 and is arranged to provide an alternating electrostatic field in advance of the leading edge of the door.

The oscillator 8 includes a tank coil 9 and tank condenser 10 in the range of 25 to 50 kilocycles. This frequency is selected as a composite in that it is high enough so that the capacitance between the antenna 5 and the channel 1 and between the antenna 5 and a grounded interfering object represented by a hand 11 is predominate over leakage resistance in determining the Voltage appearing on the antenna 5 and is still low enough in frequency so as not to interfere with radio sets that may be operating in the vicinity of the elevator.

Preferably the oscillator tank circuit coil 9 has an inductance of approximately 5 millihenries while the tank condenser 10 has a capacitance of approximately .003 mfd.

The oscillator includes a pentode driving tube 12 having its anode 13 and screen grid 14 connected directly to a positive direct current supply lead 15 which may be conveniently fed from an excited generator 16 of the elevator control system. The oscillator tube 12 is electronically coupled to the tank circuit, i. e., its cathode 17 and suppressor grid 18 are connected directly to a tap 19 of the oscillator coil 9 at a point approximately four-tenths of the length of the coil from its grounded end 20. A control grid 21 of the oscillator tube 12 is coupled through a condenser 22 to the output lead 7 of the oscillator coil 9 and is connected to ground through a grid leak resistor 23. With 250 volts applied to the supply lead 15 the oscillator 8 develops approximately 300 volts at 40 kilocycles on the output lead 7.

The output lead 7 may conveniently be carried through a grounded shield 24 to a detector circuit and coupling impedances connecting the high voltage lead 7 to the antenna wire 5. The coupling circuit comprises a resistor 25 of approximately 100,000 ohms and a balancing condenser 26 that may be mechanically coupled to the door operating mechanism so as to compensate the antenna circuit for expected changes in capacity as the door reaches or approaches the door casing as the door reaches its closed position. The detector circuit comprises a crystal rectifier 27 and a condenser 28 connected in series and the combination connected in parallel with the resistor 25.

During the operation of the device a voltage at 40 kilocycles is developed across the resistor 25 the magnitude of which voltage depends upon the ratio of the capacitance between the antenna wire 5 and the adjacent channel member 1 and a between the antenna wire 5 and a grounded object such as the hand 11. This voltage is a minimum when the space adjacent the leading edge of the door is clear and the voltage increases when the antenna wire 5 is brought into proximity with a grounded object.

The voltage developed across the resistor 25 is rectified by the crystal rectifier 27 and serves to charge the condenser 28 to a D. C. voltage proportional to the 40 kilocycle voltage appearing across the resistor 25. Since the condenser 28 of .05 mfd. is practically a short circuit with respect to 40 kilocycle current, a detector output lead 29 has impressed upon it a 40 kilocycle voltage substantially equal to the voltage appearing on the oscillator output lead 7 and, in addition, a direct current voltage negative with respect to ground corresponding to the voltage developed by the crystal rectifier 27.

This composite voltage on the output lead 29 of the detector is applied to a resistance-capacitance filter comprising a resistor 30 of approximately 2 megohms and a condenser 31 of approximately .05 mfd. This filter serves to substantially eliminate the 40 kilocycle Voltage, Which may be considered as a carrier voltage, leaving only the direct current component, i. e. the detected envelope, which is transmitted to a lead 32, the output of the filter, substantially unattenuated. This voltage on the lead 32 is capacity-coupled through a .l mfd. condenser 33 to a control grid 34 of an amplifier tube 35. The control grid 34 is also connected to ground through a relatively high adjustable resistor 36 serving as a grid resistor for the amplifier tube 35. The time constant of the condenser 33 with respect to the grid resistor 36 is adjusted so that signal voltages indicating changes in capacity between the antenna 5 and the interfering object, i. e. the variations in the detected envelope, such as the hand 11, are transmitted to the amplifier grid 34 whereas slow changes in capacitance resulting in slow changes in the voltage output of the detector occur at a rate too slow to be passed through the resistance-capacitance coupling to the amplifier grid 34.

The amplifier tube also includes a cathode 37 connected to the midpoint of a voltage divider comprising a 65,000 ohm resistor 38 and a 270 ohm resistor 39 connected between the voltage supply lead 15 and ground. A plate circuit for the amplifier tube 35 includes a 500,000 ohm plate resistor 40 connected between the supply lead 15 and a plate 41 of the tube 35. The plate 41 of the amplifier 35 is capacity coupled through a .05 mfd. coupling condenser 42 to a control grid 43 of a second amplifier tube 44. A grid return circuit for the amplifier 44 is by Way of a 3.5 megohm resistor 45 and a 27K (27 thousand) ohm resistor 46 connected in series between the grid 43 and the grounded return line. The amplifier tube 44 has its plate 47 connected through the parallel combination of a relay coil 48 and condenser 49 to the positive supply lead 15. A cathode 50 of the amplifier tube 44 is connected to the midpoint of a voltage divider comprising a 125K ohm resistor 51 and a 330 ohm resistor 52.

It may be mentioned that the polarity of the crystal rectifier 27 is such that the lead 29 is negative with respect to ground and the detector voltage goes increasingly negative as the antenna wire 5 approaches any object in its path. This negative going signal after amplification through the amplifier 35 appears as a positive going signal voltage at the input to the amplifier tube 44 thus causing the energization of the relay coil 43. Because of the time constant in the amplifier only a pulse of current is drawn by the second stage amplifier 44. Since this pulse may be of relatively short duration the condenser 49 is provided in parallel with the relay coil and arranged to momentarily store the pulse of current and discharge it into the relay coil at a rate providing reliable operation of the relay.

The resistance-capacitance coupling from the output lead 32 of the detector filter to the first amplifier 35 and from the output circuit of that amplifier to the input of the second amplifier tube 44 has the effect of transmitting only the variations in voltage occurring at a relatively rapid rate from the output of the detector to the relay coil 48. The adjustable resistor 36 provides means for adjusting the time constant of the coupling circuits so that the circuits may be adjusted to respond to any particular desired rate of change of detector output voltage signifying a particular rate of approach of the door edge to an object in its path. The resistance-capacitance coupling to and through the amplifier has the advantage of suppressing the efiFect of drift in the circuit elements thus making the circuit relatively immune to changes in temperature conditions, humidity and surface leakage currents from the antenna wire 5 either to ground or to the energized channel 1. Thus the circuit may be made very sensitive to objects appearing in the path of the door and yet be reliable in regular service operating conditions.

The circuit just described is responsive only to changes in capacitance resulting from relative movement between the moving edge of the door and objects in its path. Now and then a person is liable to be startled or frightened if a door comes at him or her, even if the door stops or retreats before touching him or her. To avoid such unpleasant incidents, it is desirable to prevent a door closing operation if a person be standing quietly in the path of a door. Therefore a photoelectric system is arranged in conjunction with the capacitance control circuit just described. The photoelectric control circuit includes a light source (not shown) arranged to project a beam of light along the path of the door to a photocell 53 mounted in a door casing and electrically arranged to actuate the relay 48 whenever the cell is darkened. The photoelectric control circuit includes a 440K ohm voltage supply resistor 54 connected between the supply lead and a junction between the grid resistors 4-5 and 46 of the amplifier tube 44. A transistor 55 has its emitter 56 connected to the junction between the resistors 45 and 46 and has its collector 57 connected to the ground return lead. A photocell 53 is connected between the emitter connection 56 and a base 58 of the transistor 55. As long as the photocell is light, indicating that the doorway is clear, the voltage appearing across the photocell is small thus reducing the voltage between the emitter 56 and base 58 thereby oermitting amplified current flow from the emitter 56 to the collector 57 and thus in efiect by-passing the 27K ohm resistor 46 and increasing the negative bias applied to the amplifier tube 44 so as to cut off current flow to the relay coil 48. When the photocell 53 is darkened, as by interrupting the light beam, the resistance of the photocell 53 increases thereby increasing the voltage between the emitter 56 and a base 58 and, increasing the resistance of this circuit, raising the voltage with respect to ground of the junction between the resistors 45 and 46 sufficiently to unbias the amplifier tube 44 and to cause it to draw current through the relay coil 48. It should be noted that the photocell and transistor are not capacity-coupled to the input circuit of the amplifier tube 4-4 and that as long as the cell is darkened the door will stay open. The relay coil 48 thus is energized as it would be if the antenna 5 were suddenly juxtaposed to a person and the door is held open while persons are passing through or standing in the doorway before the door starts to close. If a person steps into the doorway after the door starts to close or puts his hand or foot in front of the moving door, the door will be stopped even though the ray of light be not intercepted. The interconnected capacitance responsive and light sensitive circuits mutually cooperate in this way to provide safe and nonfrightening control for door closing mechanism.

The improved door protective circuits may be included in a door operating circuit such as is illustrated in Figure III. In such a circuit a door operating motor 59 is mechanically connected to the door so that a first direction of rotation of the motor closes the doors while reverse rotation opens the doors. The direction of rotation of the motor 59 is controlled by a door opening relay 60 having an operating coil 61 arranged to be energized from a lead L1 by momentary closure of a door opening push button switch 62 that connects the coil 61 directly to the lead L1. The other terminal of the coil 61 is connected through a lead 63 and door-open limit switch 64 to a return lead L2. The limit switch 64 is arranged to open the circuit when the doors reach full open position. When the coil 61 is energized it closes its contacts 65 to complete a holding circuit in parallel with the push button switch 62 to hold the relay 6%) energized after the push button switch 62 is released. The relay coil 61 may also be energized by operation of the previously described amplifier relay 48 which has its contacts 66 connected in parallel with the push button switch 62. Thus the door opening relay 69 may be energized either by operation of the door-opening pushbutton 62 or by the approach of the door to an object in its path during closing movement causing operation of the relay 48 or by the interruption of the light beam which also results in operation of the relay 48. When the relay 60 is energized it opens its contacts 67 to break the circuit to operating coil 68 of a door closing relay 69 thereby interrupting a door closing operation should one be in progress.

Operation of the door opening relay 60, by closing its contacts 70 and 71, energizes the motor 59 by connecting its lead A through the now closed contacts '70 and a resistor 72 to a lead L1 and connecting its lead B through now closed contacts 71 and resistor 73 to the supply lead L2. Motor lead C, the third lead of the three phase motor 59, is permanently connected to the line L3, the third lead of the three phase power system. This connection of the motor leads A, B, C to the supply leads L1, L2, L3 respectively produces door opening rotation of the motor 59.

The elevator doors may be closed by momentary operation of a push button switch '74 arranged to connect the operating coil 63 of the door closing relay 69 by way of the contact 67 to the lead L1. The relay 69 upon being energized closes its contacts 75 to complete a holding circuit in parallel with the push button contacts '74 and also closes its contacts 76 and 77 so as to connect motor lead B to line L1 and motor lead A to the line L2. This reversal of the connections from leads L1 and L2 to motor leads A and B results in door closing rotation of doors reach fully closed the motor 59. When the sition they open a limit switch 78 arranged in the return lead from the operating coil 68 to the line L2 thereby deenergizing the door closing relay 69.

In this circuit it will be noted that, by reason of the contacts 67 of the door opening relay 60, the door open ing operations take precedence over the door closing operations. The resistors 72 and 73 included between the lines L1 and L2 and the motor leads A and B serve to limit the maximum torque developed by the motor during starting of the doors in either direction and also limit the current flow between lines L1 and L2 that occurs when both the door opening relay 60 and the door closing relay 69 are simultaneously energized. This condition occurs momentarily when a door opening operation is started either by operation of the push button switch 62 or the safety control circuits during a door closing operation. When this happens the relay 69 is in its energized condition when the relay 60 is energized so that the simultaneous closure of contacts 70, 71, 76 and 77 short circuit the motor connections A and B until the door closing relay 69 drops out as a result of the opening of the contacts 67 of the door opening relay.

When the relay 48 is energized it holds open the normal closed contacts 74a which are in series with a push button switch 74. Thus the door is prevented from even starting to close while a person is intercepting the ray of light 91, and the liability of frightening timid persons by threatening movements of the door is avoided.

The control circuits just described, including the capacitance control for the relay 48, provide a system that has high sensitivity to relatively quick changes in capacitance between its antenna wire 5 and ground and yet is insensitive to slow changes such as may occur by reason of variation in leakage currents across the insulation or other factors tending to affect the operation of the circuit.

Various modifications of the improved circuit may be made without losing the advantages obtained by making the circuit sensitive only to relatively quick changes in capacitance resulting from the approach of the elevator door to an interfering object.

The elevator car schematically illustrated in Fig. IV has a doorway 80 over which the door 3 is slidable. The door 3 is supported by rollers 81 and 82 which roll upon a track 83 fixed to a superstructure 84. The superstructure 84 also supports the motor 59 which is connected through a belt 85 and speed reducing pulleys 86 and 87 to a horizontally extending belt 88. An arm 89 connects the door 3 to the belt 88 so that when the motor 16 turns, the door 3 is closed or opened as the motor turns in clockwise or counterclockwise direction. A projector 9t) directs a ray of light 91 across the doorway 80 to the photocell 53. The casing of insulation 2 is carried by the leading edge of the door 3.

As long as the light ray 91 continues to be interrupted by persons or objects in or passing through the doorway 80, the door 3 does not start to close. When the door Way is cleared the door starts to close, but if a person moves into the doorway by entering or leaving the car, or attempting to do so, after the door has started to close the antenna along the leading edge of the door approaches to within a few inches of the person, the motor 16 stops and reverses thus halting the movement of the door 3 and causing it to reopen. Likewise the movement of the door is halted and the door reopens if a person wishing to pass through the doorway puts a hand or a foot to the leading edge of the door.

. The foregoing specification and the accompanying drawings are intended to be regarded as merely illustrative. The safety control of the instant invention is susceptible to variation and modification within the spirit and scope of the subjoined claims.

Having described the invention, I claim:

1. In a device of the class described, in combination, an element located along the leading edge of an elevator door having a capacitance to ground which varies in accordance with the proximity of grounded objects adjacent the door leading edge, a source of high frequency electrical energy energizing said element, means connected to said element developing an electrical signal which is a function of said capacitance to ground, an amplifier, a frequency selective coupling circuit between said means and said amplifier, said coupling circuit rejecting signal components of the frequency of said source and low frequency drift signal components and passing a selected band of frequencies, and an electro mechanical translator for controlling the closing of said door, connected to said amplifier and causing the opening of said door upon the application of a signal from said means falling within said selected band of frequencies.

2. in a device of the class described, in combination, sliding door, door closing mechanism, a motor for driving said door closing mechanism, circuits for energizing said motor, an antenna carried by the leading edge of said door, means for creating an electrostatic field adjacent said antenna, means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein for acting upon said circuits to stop and reverse said motor.

3. in a device of the class described, in combination, an elevator structure having a doorway, a door movable over said doorway, mechanism for closing said door, a motor for driving said mechanism circuits for energizing said motor, an antenna carried by the leading edge of said door, means for creating an electrostatic field adjacent said antenna, projecting means for directing a ray of light across said doorway, photosensitive means located in the path of such ray of light and means nonresponsive to both gradual changes and a stable state in said electrostatic field but responsive either to sudden changes in said electrostatic field or to interruption of said ray of light for acting upon said circuits to stop and reverse said motor.

4. In a device of the class described, in combination, a sliding door, door closing mechanism, a motor for driving said door closing mechanism, circuits for energizing said motor, an antenna carried by the leading edge of said door, means for creating an electrostatic field adjacent said antenna, means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein for acting upon said circuits to stop and reverse said motor and means for preventing sudden changes in said electrostatic field resulting from relative movement of said antenna and nearby portions of the elevator structure.

5. In a device of the class described, in combination, an elevator structure having a doorway, a door movable over said doorway, mechanism for closing said door, a motor for driving said mechanism, circuits for energizing said motor, an antenna carried by the leading edge of said door, means for creating an electrostatic field adjacent said antenna, projecting means for directing a ray of light across said doorway, photosensitive means located in the path of such ray of light, means nonresponsive to both gradual changes and a stable state in said electrostatic field but responsive either to sudden changes in said electrostatic field or to interruption of said ray of light for acting upon said circuits to stop and reverse said motor, and means for compensating sudden changes in said electrostatic field resulting from relative movement of said antenna and nearby portions of the elevator structure.

6. In a device of the class described, in combination, motor energizing circuits and a motor energized thereby and capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means for creating an electrostatic field adjacent to said antenna and means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein for acting upon said motor energizing circuits to stop said motor.

7. In a device of the class described, in combination, motor energizing circuits and a motor energized thereby and capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means for creating an electrostatic field adjacent to said antenna and means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein for acting upon said motor energizing circuits to stop and reverse said motor.

8. in a device of the class described, in combination, motor energizing circuits and a motor energized thereby and capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means including an oscillator for creating an electrostatic field adjacent to said antenna and means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein for acting upon said motor energizing circuits to stop said motor.

9. in a device of the class described, in combination, motor energizing circuits and a motor energized thereby and capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means for creating an electrostatic field adjacent to said antenna, a light sensitive element so located as to be darkened by objects in the path of said door and means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein and also responsive 10 to darkening of said light sensitive element for acting upon said motor energizing circuits to stop said motor.

10. In a device of the class described, in combination, motor energizing circuits and a motor energized thereby capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means for creating an electrostatic field adjacent to said antenna, a light sensitive element so located as to be darkened by objects in the path of said door and means responsive to sudden changes in said electrostatic field and nonresponsive to both gradual changes and a stable state therein and also responsive to darkening of said light sensitive element for acting upon said motor energizing circuits to stop and reverse said motor.

ll. In a device of the class described, in combination, motor energized circuits and a motor energized thereby and capable of driving elevator door closing mechanism, an antenna located at the leading edge of a door to be closed by such mechanism, means for creating an electrostatic field adjacent to said antenna, a light sensitive element so located as to be darkened by objects in the path of said door and means responsive to changes in said electrostatic field and also responsive to darkening of said light sensitive element for acting upon said motor energizing circuits to stop and reverse said motor.

References Cited in the file of this patent I UNITED STATES PATENTS 

